Routes to action: Evidence from apraxia

Towards and away from the body: The relevance of the direction of use in the coding of object-related actions

This study examines whether the perception of an object automatically activates the representation of the direction of use of that object. To this aim, we carried out two experiments. In Experiment 1, participants were asked to explicitly categorise objects as used either away from the body (AB, for example, a hammer) or towards the body (TB, for example, a toothbrush). In Experiment 2, participants were asked to judge whether the same objects were natural or manmade. In both experiments, they were asked to respond by moving a joystick backwards (i.e., TB) or frontwards (i.e., AB). Therefore, their response could either be congruent (i.e., backward response with TB objects, frontward response with AB objects) or incongruent (i.e., backward response with AB objects, frontward response with TB objects) with the direction of object use. Results from Experiment 1 showed that in the congruent condition, participants were faster in judging the direction of object use than those in the incongruent condition (congruency effect). Crucially, results from Experiment 2 showed the presence of a congruency effect even when the direction of object use was task-irrelevant. However, this effect was found only for TB objects. These results suggest that the perception of TB objects automatically activates the direction of object use with respect to the body, thus showing evidence of direct connection between perception and action. A specific role of the body might account for different action representation processes involved in TB and AB object-related actions.

Factors Influencing Manipulation of a Familiar Object in Patients With Limb Apraxia After Stroke

Previous studies have shown that hand actions to visual objects are affected both by perceptual factors and by action goals. Our aim was to study how these processes affected hand actions in chronic stroke patients, based on whether they had limb apraxia. Twenty-two left hemisphere, chronic stroke patients were measured on neuropsychological tasks of limb apraxia, which was identified in a subgroup of 10 patients. All patients underwent testing on a separate task of making simple reach and grasp actions to a cup. Their performance was compared to a group of 18 healthy age-matched volunteers. Participants were instructed to grasp the top or bottom of a cup to either lift or turn it over so as to end with a hand position that was either comfortable or uncomfortable. This task tested the influence of the compatibility of hand–cup orientation, as well as goals driven by the end-state comfort of the hand, on action selection for object manipulation. Participants’ performance was measured in terms of error rates, and speed of initiation and reaching (movement time) to the object. The patients’ performance was significantly delayed, and error rates increased when reaching to grasp a cup under conditions of poor compatibility and end-state comfort. The subgroup of patients with apraxia showed a decreased influence of compatibility of hand interaction with the cup, with increased error rates and delayed response times, compared to patients with no apraxia and healthy volunteers. This is despite the fact they did not display significant deficits on neuropsychological tasks of real object use. The study shows that patients with apraxia have difficulties in selecting elements of object-directed actions, pertaining to both habitual and goal-directed factors.

The role of the precuneus and posterior cingulate cortex in the neural routes to action

Neural substrates of action to the object or this specific direct route, however, remain unclear, especially for the connection from the visual pathway to the motor cortex. The study examined this issue by conducting an fMRI experiment, in which two action generation tasks involving pictures of real objects (PA) and the object's nouns (NA) were used, with pictures naming (PN) and covert noun reading (NR) being the control tasks. The result showed that the model predefined for the PCC and precuneus connecting IPL to the posterior-medial frontal cortex dominated over the others (with 0.45 probability), suggesting that the PCC and the precuneus locate at the neural substrates of action to the object. Furthermore, a feasibility study suggests that the neural pathway composed of the V3/MT, precuneus, PCC, and PM (premotor cortex) forms the direct route from perception to action, which also links to the dorsal pathway so that the perception of objects bypasses the semantic ventral pathway and then directly cues actions via the affordance.

Children's scale errors are a natural consequence of learning to associate objects with actions: A computational model

Young children sometimes attempt an action on an object, which is inappropriate because of the object size-they make scale errors. Existing theories suggest that scale errors may result from immaturities in children's action planning system, which might be overpowered by increased complexity of object representations or developing teleofunctional bias. We used computational modelling to emulate children's learning to associate objects with actions and to select appropriate actions, given object shape and size. A computational Developmental Deep Model of Action and Naming (DDMAN) was built on the dual-route theory of action selection, in which actions on objects are selected via a direct (nonsemantic or visual) route or an indirect (semantic) route. As in case of children, DDMAN produced scale errors: the number of errors was high at the beginning of training and decreased linearly but did not disappear completely. Inspection of emerging object-action associations revealed that these were coarsely organized by shape, hence leading DDMAN to initially select actions based on shape rather than size. With experience, DDMAN gradually learned to use size in addition to shape when selecting actions. Overall, our simulations demonstrate that children's scale errors are a natural consequence of learning to associate objects with actions.

The evolution of cognitive models: From neuropsychology to neuroimaging and back

This paper provides a historical and future perspective on how neuropsychology and neuroimaging can be used to develop cognitive models of human brain functions. Section 1 focuses on the emergence of cognitive modelling from neuropsychology, why lesion location was considered to be unimportant and the challenges faced when mapping symptoms to impaired cognitive processes. Section 2 describes how established cognitive models based on behavioural data alone cannot explain the complex patterns of distributed brain activity that are observed in functional neuroimaging studies. This has led to proposals for new cognitive processes, new cognitive strategies and new functional ontologies for cognition. Section 3 considers how the integration of data from lesion, behavioural and functional neuroimaging studies of large cohorts of brain damaged patients can be used to determine whether inter-patient variability in behaviour is due to differences in the premorbid function of each brain region, lesion site or cognitive strategy. This combination of neuroimaging and neuropsychology is providing a deeper understanding of how cognitive functions can be lost and re-learnt after brain damage - an understanding that will transform our ability to generate and validate cognitive models that are both physiologically plausible and clinically useful.

Tool Use and Generalized Motor Programs: We All Are Natural Born Poly-Dexters

For most people, human tool use is inextricably entwined with manual dexterity. This folk belief is widespread among scientists too. In this line, human tool use is based on motor programs about how the hand interacts with tools, implying that the use of end-effectors other than the hand should generate motor control difficulties (e.g., inability to reproduce a specific tool-use action over time), because these so-called programs characterize the spatiotemporal parameters of hand movements, but not of other end-effectors. To test this, we asked participants to perform three tool-use actions (e.g., pounding a nail) with four end-effectors (i.e., right foot, right elbow, left hand, right hand). We show that participants not only spontaneously performed the tool-use actions effectively, but also crucially kept tools’ spatiotemporal parameters constant among the end-effectors. This phenomenon, which we call poly-dexterity, is at odds with the view that the human brain stores hand-centered motor programs for tool use. Poly-dexterity is instead consistent with the idea that, once the tool-use action is formed mentally, general motor programs can be applied to a variety of end-effectors. Reversing the usual evolutionary perspective, our findings support that, in the course of evolution, manual dexterity has come after tool-use skills.

Dissociative effects of viewpoint and semantic priming on action and semantic decisions: Evidence for dual routes to action from vision

This article reports evidence that two variables—object viewpoint and semantic priming—differentially affect action and semantic decisions to objects. Changing the viewing angle of an object, so that its graspable parts are oriented away from observers, disrupted action decisions but had little effect on semantic categorization. In contrast, semantic priming influenced semantic categorization and object naming, but not action decisions. Action priming, however, did not affect performance. These selective effects are consistent with the existence of separate semantic and direct (nonsemantic) routes to action from vision.

Treatments and technologies in the rehabilitation of apraxia and action disorganisation syndrome: A review

BACKGROUND: Apraxia and Action Disorganisation Syndrome are characterised by an inability to use tools and carry out ordered sequences of movements in the absence of motor or sensory impairment. To date treatment for these complex but debilitating conditions has received little attention.

OBJECTIVES: To provide an overview of apraxia and action disorganisation syndrome and its treatment, providing a state of the art summary for practitioners including likely future therapeutic directions.

METHOD: Review of apraxia literature and treatment studies collated from internet searches involving MEDLINE, PubMed, PyscINFO and Google Scholar as well as the author’s own catalogue.

RESULTS: Evidence for current restitution and compensatory approaches is critically reviewed, with limited evidence to date in support of either method. Strategy training is the most promising intervention type with no support for sensory and exploratory interventions, practice effects only for direct task-specific training, and modest support for gestural training.

CONCLUSIONS: Larger controlled studies are needed but evidence is sufficient to indicate certain approaches over others. Advances in assistive technology have not translated into mainstream therapy but future interventions are likely to require a model-based approach which embraces current technologies in order to provide a more accessible, effective and cost-efficient approach to rehabilitation.

Factors influencing planning of a familiar grasp to an object: what it is to pick a cup

We assessed the factors influencing the planning of actions required to manipulate one of two everyday objects with matching dimensions but openings at opposite ends: a cup and a vase. We found that, for cups, measures of movement preparation to reach and grasp the object were influenced by whether the grasp was made to the functional part of the object (wide opening) and whether the action would end in a supinated as opposed to a pronated grasp. These factors interacted such that effects of hand posture were found only when a less familiar grasp was made to the non-functional part of the cup (the base). These effects were not found with the vase, which has a less familiar location for grasping. We interpret the results in terms of a parallel model of action selection, modulated by both the familiarity of the grasp to a part of the object, likely to reflect object 'affordances' and the end state comfort of the action.

The involvement of the dorsal stream in processing implied actions between paired objects: A TMS study

Perceiving and selecting the action possibilities (affordances) provided by objects is an important challenge to human vision, and is not limited to single-object scenarios. Xu et al. (2015) identified two effects of implied actions between paired objects on response selection: an inhibitory effect on responses aligned with the passive object in the pair (e.g. a bowl) and an advantage associated with responses aligned with the active objects (e.g. a spoon). The present study investigated the neurocognitive mechanisms behind these effects by examining the involvement of the ventral (vision for perception) and the dorsal (vision for action) visual streams, as defined in Goodale and Milner's (1992) two visual stream theory. Online repetitive transcranial magnetic stimulation (rTMS) applied to the left anterior intraparietal sulcus (aIPS) reduced both the inhibitory effect of implied actions on responses aligned with the passive objects and the advantage of those aligned with the active objects, but only when the active objects were contralateral to the stimulation. rTMS to the left lateral occipital areas (LO) did not significantly alter the influence of implied actions. The results reveal that the dorsal visual stream is crucial not only in single-object affordance processing, but also in responding to implied actions between objects.

Intervention Effectiveness: Evidence from a Case Study of Ideomotor and Ideational Apraxia

This paper considers the characteristics of apraxia and presents a case study which explores the effectiveness of tactile and kinaesthetic stimulation as an intervention strategy, in addition to visual and verbal mediation input, in the rehabilitation of a man with ideomotor and ideational apraxia following a head injury. Using an ABA design, quantitative measures were used to monitor change in motor performance. The results indicated some significant differences in measured performances between baseline and intervention phases and provided limited evidence of the effectiveness of additional sensory input. The implications for occupational therapy are discussed as are the limitations of the study.

Limb apraxia and the "affordance competition hypothesis"

Limb apraxia, a disorder of higher order motor control, has long been a challenge for clinical assessment and understanding (Leiguarda and Marsden, 2000). The deficits originally described in limb apraxia (Liepmann, 1920) have been classified by the nature of the errors made by the patients leading to, namely, ideational and ideomotor apraxia. The dual stream hypothesis (Goodale and Milner, 1992) has been used to explain these categories: ideational apraxia is thought to relate to a deficit in the concept of a movement (coded in the ventral stream). Patients have difficulty using objects, sequencing actions to interact with them or pantomiming their use. Ideomotor apraxia, on the other hand, is thought to arise from problems in the accurate implementation of movements within the dorsal stream. One of the limitations on understanding apraxia is the failure by the clinical literature to draw on knowledge of the factors determining actions in the environment. Here we emphasize the role of affordance. There is much recent work indicating that our responses to stimuli are strongly influenced by the actions that the objects "afford", based on their physical properties and the intentions of the actor (e.g., Tucker and Ellis, 1998). The concept of affordance, originally suggested by Gibson (1979) has been incorporated in a recent model of interactive behavior that draws from findings in non-human primates, namely the "affordance competition hypothesis" (Cisek, 2007). This postulates that interactive behavior arises by a process of competition between possible actions elicited by the environment. In this paper we argue that "affordance competition" may play a role in apraxia. We review evidence that at least some aspects of apraxia may reflect an abnormal sensitivity to competition when multiple affordances are present (Riddoch et al., 1998) and/or a poor ability to exert cognitive control over this competition when it occurs. This framework suggests a new way of conceptualizing deficits in apraxia which invites further investigations in the field.

Mechanisms underlying selecting objects for action

We assessed the factors which affect the selection of objects for action, focusing on the role of action knowledge and its modulation by distracters. Fourteen neuropsychological patients and 10 healthy aged-matched controls selected pairs of objects commonly used together among distracters in two contexts: with real objects and with pictures of the same objects presented sequentially on a computer screen. Across both tasks, semantically related distracters led to slower responses and more errors than unrelated distracters and the object actively used for action was selected prior to the object that would be passively held during the action. We identified a sub-group of patients (N = 6) whose accuracy was 2SDs below the controls performances in the real object task. Interestingly, these impaired patients were more affected by the presence of unrelated distracters during both tasks than intact patients and healthy controls. Note that the impaired patients had lesions to left parietal, right anterior temporal and bilateral pre-motor regions. We conclude that: (1) motor procedures guide object selection for action, (2) semantic knowledge affects action-based selection, (3) impaired action decision making is associated with the inability to ignore distracting information and (4) lesions to either the dorsal or ventral visual stream can lead to deficits in making action decisions. Overall, the data indicate that impairments in everyday tasks can be evaluated using a simulated computer task. The implications for rehabilitation are discussed.

Selecting object pairs for action: Is the active object always first?

Perception is linked to action via two routes: a direct route based on affordance information in the environment and an indirect route based on semantic knowledge about objects. The present study explored the factors modulating the recruitment of the two routes, in particular which factors affecting the selection of paired objects. In Experiment 1, we presented real objects among semantically related or unrelated distracters. Participants had to select two objects that can interact. The presence of distracters affected selection times, but not the semantic relations of the objects with the distracters. Furthermore, participants first selected the active object (e.g. teaspoon) with their right hand, followed by the passive object (e.g. mug), often with their left hand. In Experiment 2, we presented pictures of the same objects with no hand grip, congruent or incongruent hand grip. Participants had to decide whether the two objects can interact. Action decisions were faster when the presentation of the active object preceded the presentation of the passive object, and when the grip was congruent. Interestingly, participants were slower when the objects were semantically but not functionally related; this effect increased with congruently gripped objects. Our data showed that action decisions in the presence of strong affordance cues (real objects, pictures of congruently gripped objects) relied on sensory-motor representation, supporting the direct route from perception-to-action that bypasses semantic knowledge. However, in the case of weak affordance cues (pictures), semantic information interfered with action decisions, indicating that semantic knowledge impacts action decisions. The data support the dual-route account from perception-to-action.

Neural correlates of transitive and intransitive action imitation: an investigation using voxel-based morphometry

The ability to reproduce visually presented actions has been studied through neuropsychological observations of patients with ideomotor apraxia. These studies include attempts to understand the neural basis of action reproduction based on lesion-symptom mapping in different patient groups. While there is a convergence of evidence that areas in the parietal and frontal lobes within the left hemisphere are involved in the imitation of a variety of actions, questions remain about whether the results generalize beyond the imitation of tool use and whether the presence of a strong grasp component of the action is critical. Here we used voxel-based lesion-symptom mapping to assess the neural substrates of imitating meaningful (familiar, MF) and meaningless (unfamiliar, ML) tool-related (transitive) and non-tool related (intransitive) actions. The analysis showed that the left parietal cortex was involved in the imitation of transitive gestures, regardless of whether they were meaningful or not. In addition there was poor reproduction of meaningless actions (both transitive and intransitive) following damage of the right frontal cortex. These findings suggest a role of right frontal regions in processing of unfamiliar actions.

Tool use disorders after left brain damage

In this paper we review studies that investigated tool use disorders in left-brain damaged (LBD) patients over the last 30 years. Four tasks are classically used in the field of apraxia: Pantomime of tool use, single tool use, real tool use and mechanical problem solving. Our aim was to address two issues, namely, (1) the role of mechanical knowledge in real tool use and (2) the cognitive mechanisms underlying pantomime of tool use, a task widely employed by clinicians and researchers. To do so, we extracted data from 36 papers and computed the difference between healthy subjects and LBD patients. On the whole, pantomime of tool use is the most difficult task and real tool use is the easiest one. Moreover, associations seem to appear between pantomime of tool use, real tool use and mechanical problem solving. These results suggest that the loss of mechanical knowledge is critical in LBD patients, even if all of those tasks (and particularly pantomime of tool use) might put differential demands on semantic memory and working memory.

The Neural Selection and Integration of Actions and Objects: An fMRI Study

There is considerable evidence that there are anatomically and functionally distinct pathways for action and object recognition. However, little is known about how information about action and objects is integrated. This study provides fMRI evidence for task-based selection of brain regions associated with action and object processing, and on how the congruency between the action and the object modulates neural response. Participants viewed videos of objects used in congruent or incongruent actions and attended either to the action or the object in a one-back procedure. Attending to the action led to increased responses in a fronto-parietal action-associated network. Attending to the object activated regions within a fronto-inferior temporal network. Stronger responses for congruent action–object clips occurred in bilateral parietal, inferior temporal, and putamen. Distinct cortical and thalamic regions were modulated by congruency in the different tasks. The results suggest that (i) selective attention to action and object information is mediated through separate networks, (ii) object–action congruency evokes responses in action planning regions, and (iii) the selective activation of nuclei within the thalamus provides a mechanism to integrate task goals in relation to the congruency of the perceptual information presented to the observer.

Re-examining the gesture engram hypothesis. New perspectives on apraxia of tool use

In everyday life, we are led to reuse the same tools (e.g., fork, hammer, coffee-maker), raising the question as to whether we have to systematically recreate the idea of the manipulation which is associated with these tools. The gesture engram hypothesis offers a straightforward answer to this issue, by suggesting that activation of gesture engrams provides a processing advantage, avoiding portions of the process from being reconstructed de novo with each experience. At first glance, the gesture engram hypothesis appears very plausible. But, behind this beguiling simplicity lies a set of unresolved difficulties: (1) What is the evidence in favour of the idea that the mere observation of a tool is sufficient to activate the corresponding gesture engram? (2) If tool use can be supported by a direct route between a structural description system and gesture engrams, what is the role of knowledge about tool function? (3) And, more importantly, what does it mean to store knowledge about how to manipulate tools? We begin by outlining some of the main formulations of the gesture engram hypothesis. Then, we address each of these issues in more detail. To anticipate our discussion, the gesture engram hypothesis appears to be clearly unsatisfactory, notably because of its incapacity to offer convincing answers to these different issues. We conclude by arguing that neuropsychology may greatly benefit from adopting the hypothesis that the idea of how to manipulate a tool is recreated de novo with each experience, thus opening interesting perspectives for future research on apraxia.

fMRI-adaptation evidence of overlapping neural representations for objects related in function or manipulation

Sensorimotor-based theories of semantic memory contend that semantic information about an object is represented in the neural substrate invoked when we perceive or interact with it. We used fMRI adaptation to test this prediction, measuring brain activation as participants read pairs of words. Pairs shared function (flashlight-lantern), shape (marble-grape), both (pencil-pen), were unrelated (saucer-needle), or were identical (drill-drill). We observed adaptation for pairs with both function and shape similarity in left premotor cortex. Further, degree of function similarity was correlated with adaptation in three regions: two in the left temporal lobe (left medial temporal lobe, left middle temporal gyrus), which has been hypothesized to play a role in mutimodal integration, and one in left superior frontal gyrus. We also found that degree of manipulation (i.e., action) and function similarity were both correlated with adaptation in two regions: left premotor cortex and left intraparietal sulcus (involved in guiding actions). Additional considerations suggest that the adaptation in these two regions was driven by manipulation similarity alone; thus, these results imply that manipulation information about objects is encoded in brain regions involved in performing or guiding actions. Unexpectedly, these same two regions showed increased activation (rather than adaptation) for objects similar in shape. Overall, we found evidence (in the form of adaptation) that objects that share semantic features have overlapping representations. Further, the particular regions of overlap provide support for the existence of both sensorimotor and amodal/multimodal representations.

The influence of action perception on object recognition: a developmental study

Two experiments explored the existence and the development of relations between action representations and object representations. A priming paradigm was used in which participants viewed an action pantomime followed by the picture of a tool, the tool being either associated or unassociated with the preceding action. Overall, we observed that the perception of an action pantomime can facilitate the recognition of a corresponding tool. Experiment 1 was based on a naming task and was conducted with 9- to 12-year-old children and a group of young adults. While substantial priming effects were obtained for all age groups, they were especially important for the youngest participants. Smaller priming effects were obtained in Experiment 2, using a categorization task and conducted on 5- to 11-year-old children and young adults, but again the results suggest that these action priming effects diminish with increasing age. Implications of these results for the organization and development of conceptual knowledge are discussed.

Retrieval by a patient with apraxia of sensorimotor information from visually presented objects

Motor representations are reported to be implicitly evoked when one observes manipulatable objects (action potentiation). The relationship was examined between action potentiation and pantomime deficit in apraxia. Participants responded to line drawings of manipulatable objects with either the left or right hand, according to the color of the stimulus. In normal participants (N= 10, four women, six men, M age = 28.5 yr., SD = 5.6), responses were faster when the orientation of the stimulus was compatible with the response-hand grasp. However, the apraxic patient did not exhibit this compatibility effect. On a control task in which a nonobject (circle) was presented, all participants exhibited the compatibility effect. These results indicated that the apraxic patient was impaired in evoking motor representation associated with objects. Thus, in some cases, apraxic disorders may be attributable to a deficit in retrieving object-specific information for manipulation.

Are different affordances subserved by different neural pathways?

This paper questions whether affordances are allied exclusively to dorsal stream processing within the visual system, or whether in fact different affordances are subserved by functionally independent neural pathways. Using case study evidence from patients with various visual pathologies, I argue that affordances can be categorised into type based upon their respective neurological underpinning. Such categorisation has implications for the extent to which affordances are consciously perceived or non-consciously 'picked up' within the optic array, as well as whether they indicate merely potentials for action or provide necessary information in the actualisation of behaviour.

Semantic activation in action planning

Four experiments investigated activation of semantic information in action preparation. Participants either prepared to grasp and use an object (e.g., to drink from a cup) or to lift a finger in association with the object's position following a go/no-go lexical-decision task. Word stimuli were consistent to the action goals of the object use (Experiment 1) or to the finger lifting (Experiment 2). Movement onset times yielded a double dissociation of consistency effects between action preparation and word processing. This effect was also present for semantic categorizations (Experiment 3), but disappeared when introducing a letter identification task (Experiment 4). In sum, our findings indicate that action semantics are activated selectively in accordance with the specific action intention of an actor.

Direct and indirect effects of action on object classification

We report three experiments in which name verification responses to either objects (Experiments 1 and 2) or hand movements (Experiment 3) were compared with action decisions, where participants verified whether an object is typically used in the way described by a verbal label. In Experiments 1 and 2, we report that action decisions show more consistent and larger effects of the congruency of either a handgrip or a type of movement than do name verification responses, although there was some effect of the congruency of the handgrip on name verification. In Experiment 3, we demonstrate that the congruency of the object being moved affects both action and name verification responses to hand movements. We discuss the]data relative to accounts of how actions and names are accessed by visually presented objects and in relation to work on the information called upon in classification tasks.

Action priming by briefly presented objects

Three experiments investigated how visual objects prime the actions they afford. The principal concern was whether such visuomotor priming depends upon a concurrent visual input--as would be expected if it is mediated by on-line dorsal system processes. Experiment 1 showed there to be essentially identical advantages for making afforded over non-afforded responses when these were made to objects still in view and following brief (30 or 50 ms) object exposures that were backward masked. Experiment 2 showed that affordance effects were also unaffected by stimulus degradation. Finally, Experiment 3 showed there to be statistically equal effects from images of objects and their names. The results suggest that an active object representation is sufficient to generate affordance compatibility effects based on associated actions, whether or not the object is concurrently visible.

Praxic skills in down and mentally retarded adults: Evidence for multiple action routes

Functional relationships between praxic performance and visual recognition ability of mentally retarded adults are discussed, in an attempt to integrate findings from developmental disorders of action with those described in the adult literature. Three groups of participants took part in the study: adults with Down's syndrome (D), Mentally Retarded adults (MR), and mental age-matched controls (C). Three experiments were conducted. A gesture production task (Experiment 1) aimed to test ability to demonstrate the object use under three different experimental conditions: first, participants could only see the objects; second, they were allowed to see as well as to touch the objects; and third, participants were presented with the object names. An object decision task (Experiment 2) assessed the participants' ability to access structural descriptions of objects from vision. An imitation task (Experiment 3) was administered in order to test for the presence of Ideomotor Apraxia. Our results suggest that the two pathological samples may use different processing routes to action.

Privileged access to action for objects relative to words

We compared action (pour or twist?) and contextual/semantic (found in kitchen?) decisions made to pictures of objects, nonobjects, and words. Although there was no advantage for objects over words in contextual/semantic decisions, there was an advantage for objects over words and nonobjects in action decisions. For objects, both action and contextual/semantic decisions were faster than naming; for words, the opposite occurred. These results extend the early results of Potter and Faulconer (1975) that there is privileged access to semantic memory for objects relative to that for words and privileged access to phonology for words. Our data suggest that, for objects, there is privileged access to action knowledge rather than to all forms of semantic knowledge and that this is contingent on learned associations between objects and actions.

How comparable are tests of apraxia?

OBJECTIVE

To compare commonly used tests for the diagnosis of apraxia.

MEASURES

People with unilateral left hemisphere lesions, diagnosed with apraxia, were compared in their scoring on commonly used tests for apraxia (n = 17).

SETTING

Rivermead Rehabilitation Centre, Oxford, England, a specialist inpatient neurological unit.

RESULTS

Production moment correlations were low, or did not reach significance level between three tests for ideomotor apraxia (r = 0.46 p < 0.05 one-tailed test, r = 0.005 NS, r = -0.23 NS, df = 15). Six of the seventeen apraxic patients scored above cut-off point on one test, but below cut-off point on others, indicating that commonly used tests for apraxia may not be reliable for diagnosis if used singly. Internal consistency within tests was also variable (Cronbach's alpha 0.72, 0.85, 0.85).

CONCLUSION

The commonly used tests for apraxia may identify different people as 'apraxic', possibly by eliciting different aspects of apraxia and identifying potential subtypes of the condition. The use of multiple tests is, therefore, recommended in order to identify people with apraxia. The need for repeat reliability studies for apraxia assessments, together with a search for a 'gold standard' test is apparent.

Grasping objects by their handles: a necessary interaction between cognition and action

Research has illustrated dissociations between "cognitive" and "action" systems, suggesting that different representations may underlie phenomenal experience and visuomotor behavior. However, these systems also interact. The present studies show a necessary interaction when semantic processing of an object is required for an appropriate action. Experiment 1 demonstrated that a semantic task interfered with grasping objects appropriately by their handles, but a visuospatial task did not. Experiment 2 assessed performance on a visuomotor task that had no semantic component and showed a reversal of the effects of the concurrent tasks. In Experiment 3, variations on concurrent word tasks suggested that retrieval of semantic information was necessary for appropriate grasping. In all, without semantic processing, the visuomotor system can direct the effective grasp of an object, but not in a manner that is appropriate for its use.